Subsurface safety valves are commonly employed in oil or gas production wells to enable the operator to close off the flow of produced fluids from the well, if desired. A conventional subsurface safety valve assembly is shown in FIG. 1A and generally designated 10. The safety valve assembly 10 is positioned in a completed wellbore 12 penetrating a subterranean formation 14 from an earthen surface 16. It is understood that the earthen surface 16 may be substantially covered by water in a marine environment or the earthen surface 16 may be substantially exposed to the atmosphere in a land environment. A casing 18 extends the length of the wellbore 12, abutting the wellbore face 20, and a production tubing string 22 extends coaxially through the wellbore 12 within the casing 18. The production tubing string 22 has an outside diameter which is substantially less than the inside diameter of the casing 18, thereby defining a production tubing annulus 24 between the casing 18 and the production tubing string 22. The production tubing string 22 is substantially straight and relatively rigid, typically formed from multiple segments of straight rigid steel pipe which are joined together end to end. An upper segment 26a and a lower segment 26b of the production tubing string 22 are shown, having lower and upper threaded female connectors 28a, 28b, respectively, at their adjacent ends for joining the upper and lower segments 26a, 26b with the subsurface equipment, as shown and described below.
The safety valve assembly 10 includes a surface controlled subsurface safety valve (SCSSV) 30 and a control line 32 for operation of the SCSSV 30. The SCSSV 30 comprises a plurality of components, including a housing 34, a flapper 36, a flapper pivot hinge 38, a flapper seat 40, upper and lower threaded male connectors 44a, 44b, and an actuator 46. The SCSSV 30 is positioned in the production tubing string 22 by connecting the upper and lower male connectors 44a, 44b to the lower and upper female connectors 28a, 28b. In particular, the upper male connector 44a of the housing 34 is threaded into the lower female connector 28a of the upper tubing segment 26a and the lower male connector 44b of the housing 34 is threaded into the upper female connector 28b of the lower tubing segment 26b to form sealed joints 48a, 48b, which effectively integrate the SCSSV 30 into the production tubing string 22.
The open interior of the housing 34 defines an internal fluid passageway 50. The flapper 36, flapper pivot hinge 38, and flapper seat 40 are positioned in the internal fluid passageway 50. FIG. 1A shows the safety valve assembly 10 in the opened position, wherein the flapper 36 is maintained in a down position within the internal fluid passageway 50, substantially flush against the interior wall 52 of the housing 34 on the same side as the flapper pivot hinge 38. The internal fluid passageway 50 has an inside diameter substantially equal to the inside diameter of the production tubing string 22, such that the passageway 50 and interior of the production tubing string 22 form a single integrated continuous flowpath through the SCSSV 30 and production tubing string 22. For definitional purposes, the SCSSV 30, as described above, is deemed to be positioned in the production tubing string 22 insofar as the SCSSV 30 is integral with the production tubing string 22.
The actuator 46 is encased in the housing 34 and receives the subsurface end of the control line 32, which extends through the production tubing annulus 24 from the housing 34 to the surface 16. The surface end of the control line 32 is received by a valve controller 54 at the surface 16. The control line 32 enables communication of operating instructions from the valve controller 54 to the actuator 46 of the SCSSV 30 in a manner described in greater detail below.
Referring to FIG. 1B, the safety valve assembly 10 is shown in a closed position, wherein the flapper 36 has been pivotally rotated about the pivot hinge 38. The free end of the flapper 36, which is opposite the end of the flapper 36 connected to the pivot hinge 38, is in an up position in sealed abutment with the flapper seat 40, which is located on the opposite side of the interior wall 52 from the pivot hinge 38. The flapper 36 has a cross section substantially identical to that of the internal fluid passageway 50 to form a fluid seal across the flowpath through the SCSSV 30 and the production tubing string 22. As such, the closed position of the safety valve assembly 10 blocks fluid flow through the internal fluid passageway 50 and integral production tubing string 22.
Transitioning the safety valve assembly 10 between the opened position of FIG. 1A and the closed position of FIG. 1B is effected by an operator at the surface 16 who communicates a transition instruction to the SCSSV 30 via the control line 32, using the valve controller 54. The valve controller 54 is a conventional pressurizing means which maintains a pressurizable fluid in the control line 32 at predetermined pressure levels. The control line 32 is in pressure communication with the actuator 46, which is a conventional mechanical device, such as a spring-loaded latch, for alternately retaining or releasing the flapper 36. The actuator 46 maintains the flapper 36 in the down position (and correspondingly the safety valve assembly 10 in the opened position) in response to a first predetermined pressure level. When the operator wishes to transition the safety valve assembly 10 to the closed position, the operator instructs the valve controller 54 to change the pressure level of the pressurizable fluid in the control line 32 to a second predetermined pressure level. The second predetermined pressure level is communicated to the actuator 46, which reverses the position of the flapper 36 and correspondingly the position of the safety valve assembly 10.
A specific operational embodiment of the safety valve assembly 10 is illustrated below by example. The valve controller 54 is initially set by the operator at a first setting, which corresponds to the opened position of the safety valve assembly 10 shown in FIG. 1A. At the first setting, the valve controller 54 is programmed to pressurize a hydraulic fluid which fills the control line 32 and maintain the hydraulic fluid pressure at a level which is substantially above the hydrostatic pressure of the hydraulic fluid. The control line 32 communicates this elevated pressure level to the actuator 46, which mechanically maintains the flapper 36 in the down position in response to the elevated pressure level. The operator transitions the position of the safety valve assembly 10 by setting the valve controller 54 to a second setting, which corresponds to the closed position of the safety valve assembly 10 shown in FIG. 1B. At the second setting, the valve controller 54 is programmed to cease pressurizing the hydraulic fluid in the control line 32 and to depressurize the hydraulic fluid. As a result, the pressure level in the control line drops to the hydrostatic pressure of the hydraulic fluid. The control line 32 communicates this reduced pressure level to the actuator 46, which mechanically releases the flapper 36 in response to the reduced pressure level, enabling the flapper 36 to move to the up position.
Since the safety valve assembly 10 is integrally assembled with the production tubing string 22, the safety valve assembly 10 is typically installed simultaneous with installation of the production tubing string 22 during completion of the well. The installed safety valve assembly 10 is generally effective for its intended purpose. However, the safety valve assembly 10 can experience failure, most commonly resulting from a breach in the integrity of the control line 32, failure of the control line 32, or failure of a mechanical component of the SCSSV 30. Remediation of a failure requires killing the well, mobilizing a workover rig, pulling the production tubing string 22 and the integral safety valve assembly 10 from the wellbore 12, repairing or replacing the failed safety valve assembly 10, and returning the production tubing string 22 and operational safety valve assembly 10 to the wellbore 12. It is apparent that remediation of a failure requires the availability of a workover rig and is extremely costly and time consuming. The present invention recognizes a need for a less costly and time consuming, yet effective, means for remedying a subsurface safety valve assembly failure.
Accordingly, it is an object of the present invention to provide a subsurface safety valve assembly which is remedially deployable in a hydrocarbon production well. More particularly, it is an object of the present invention to provide a remedially deployable subsurface safety valve assembly which can be installed without replacing the failed subsurface safety valve assembly already present in the wellbore. It is another object of the present invention to provide a remedially deployable subsurface safety valve assembly which integrates the newly deployed subsurface safety valve assembly into the structure of the failed subsurface safety valve assembly retained in the wellbore. It is still another object of the present invention to provide a remedially deployable subsurface safety valve assembly which can be installed without pulling the production tubing string from the wellbore. It is yet another object of the present invention to provide a remedially deployable subsurface safety valve assembly which can be installed without killing the well during installation. It is a further object of the present invention to provide a remedially deployable subsurface safety valve assembly which can be installed without using a workover rig. These objects and others are achieved in accordance with the invention described hereafter.